NAME

SYNOPSIS

DESCRIPTION

Fontconfig is a library designed to provide system-wide font
configuration, customization and application access.

FUNCTIONALOVERVIEW

Fontconfig contains two essential modules, the configuration module
which builds an internal configuration from XML files and the matching
module which accepts font patterns and returns the nearest matching
font.
FONTCONFIGURATION
The configuration module consists of the FcConfig datatype, libexpat
and FcConfigParse which walks over an XML tree and amends a
configuration with data found within. From an external perspective,
configuration of the library consists of generating a valid XML tree
and feeding that to FcConfigParse. The only other mechanism provided to
applications for changing the running configuration is to add fonts and
directories to the list of application-provided font files.
The intent is to make font configurations relatively static, and shared
by as many applications as possible. It is hoped that this will lead to
more stable font selection when passing names from one application to
another. XML was chosen as a configuration file format because it
provides a format which is easy for external agents to edit while
retaining the correct structure and syntax.
Font configuration is separate from font matching; applications needing
to do their own matching can access the available fonts from the
library and perform private matching. The intent is to permit
applications to pick and choose appropriate functionality from the
library instead of forcing them to choose between this library and a
private configuration mechanism. The hope is that this will ensure that
configuration of fonts for all applications can be centralized in one
place. Centralizing font configuration will simplify and regularize
font installation and customization.
FONTPROPERTIES
While font patterns may contain essentially any properties, there are
some well known properties with associated types. Fontconfig uses some
of these properties for font matching and font completion. Others are
provided as a convenience for the applications' rendering mechanism.
Property Type Description
--------------------------------------------------------------
family String Font family names
familylang String Languages corresponding to each family
style String Font style. Overrides weight and slant
stylelang String Languages corresponding to each style
fullname String Font full names (often includes style)
fullnamelang String Languages corresponding to each fullname
slant Int Italic, oblique or roman
weight Int Light, medium, demibold, bold or black
size Double Point size
width Int Condensed, normal or expanded
aspect Double Stretches glyphs horizontally before hinting
pixelsize Double Pixel size
spacing Int Proportional, dual-width, monospace or charcell
foundry String Font foundry name
antialias Bool Whether glyphs can be antialiased
hinting Bool Whether the rasterizer should use hinting
hintstyle Int Automatic hinting style
verticallayout Bool Use vertical layout
autohint Bool Use autohinter instead of normal hinter
globaladvance Bool Use font global advance data
file String The filename holding the font
index Int The index of the font within the file
ftface FT_Face Use the specified FreeType face object
rasterizer String Which rasterizer is in use
outline Bool Whether the glyphs are outlines
scalable Bool Whether glyphs can be scaled
scale Double Scale factor for point->pixel conversions
dpi Double Target dots per inch
rgba Int unknown, rgb, bgr, vrgb, vbgr,
none - subpixel geometry
lcdfilter Int Type of LCD filter
minspace Bool Eliminate leading from line spacing
charset CharSet Unicode chars encoded by the font
lang String List of RFC-3066-style languages this
font supports
fontversion Int Version number of the font
capability String List of layout capabilities in the font
embolden Bool Rasterizer should synthetically embolden the font
FONTMATCHING
Fontconfig performs matching by measuring the distance from a provided
pattern to all of the available fonts in the system. The closest
matching font is selected. This ensures that a font will always be
returned, but doesn't ensure that it is anything like the requested
pattern.
Font matching starts with an application constructed pattern. The
desired attributes of the resulting font are collected together in a
pattern. Each property of the pattern can contain one or more values;
these are listed in priority order; matches earlier in the list are
considered "closer" than matches later in the list.
The initial pattern is modified by applying the list of editing
instructions specific to patterns found in the configuration; each
consists of a match predicate and a set of editing operations. They are
executed in the order they appeared in the configuration. Each match
causes the associated sequence of editing operations to be applied.
After the pattern has been edited, a sequence of default substitutions
are performed to canonicalize the set of available properties; this
avoids the need for the lower layers to constantly provide default
values for various font properties during rendering.
The canonical font pattern is finally matched against all available
fonts. The distance from the pattern to the font is measured for each
of several properties: foundry, charset, family, lang, spacing,
pixelsize, style, slant, weight, antialias, rasterizer and outline.
This list is in priority order -- results of comparing earlier elements
of this list weigh more heavily than later elements.
There is one special case to this rule; family names are split into two
bindings; strong and weak. Strong family names are given greater
precedence in the match than lang elements while weak family names are
given lower precedence than lang elements. This permits the document
language to drive font selection when any document specified font is
unavailable.
The pattern representing that font is augmented to include any
properties found in the pattern but not found in the font itself; this
permits the application to pass rendering instructions or any other
data through the matching system. Finally, the list of editing
instructions specific to fonts found in the configuration are applied
to the pattern. This modified pattern is returned to the application.
The return value contains sufficient information to locate and
rasterize the font, including the file name, pixel size and other
rendering data. As none of the information involved pertains to the
FreeType library, applications are free to use any rasterization engine
or even to take the identified font file and access it directly.
The match/edit sequences in the configuration are performed in two
passes because there are essentially two different operations necessary
-- the first is to modify how fonts are selected; aliasing families and
adding suitable defaults. The second is to modify how the selected
fonts are rasterized. Those must apply to the selected font, not the
original pattern as false matches will often occur.
FONTNAMES
Fontconfig provides a textual representation for patterns that the
library can both accept and generate. The representation is in three
parts, first a list of family names, second a list of point sizes and
finally a list of additional properties:
<families>-<point sizes>:<name1>=<values1>:<name2>=<values2>...
Values in a list are separated with commas. The name needn't include
either families or point sizes; they can be elided. In addition, there
are symbolic constants that simultaneously indicate both a name and a
value. Here are some examples:
Name Meaning
----------------------------------------------------------
Times-12 12 point Times Roman
Times-12:bold 12 point Times Bold
Courier:italic Courier Italic in the default size
Monospace:matrix=1 .1 0 1 The users preferred monospace font
with artificial obliquing
The '\', '-', ':' and ',' characters in family names must be preceeded
by a '\' character to avoid having them misinterpreted. Similarly,
values containing '\', '=', '_', ':' and ',' must also have them
preceeded by a '\' character. The '\' characters are stripped out of
the family name and values as the font name is read.

DEBUGGINGAPPLICATIONS

To help diagnose font and applications problems, fontconfig is built
with a large amount of internal debugging left enabled. It is
controlled by means of the FC_DEBUG environment variable. The value of
this variable is interpreted as a number, and each bit within that
value controls different debugging messages.
Name Value Meaning
---------------------------------------------------------
MATCH 1 Brief information about font matching
MATCHV 2 Extensive font matching information
EDIT 4 Monitor match/test/edit execution
FONTSET 8 Track loading of font information at startup
CACHE 16 Watch cache files being written
CACHEV 32 Extensive cache file writing information
PARSE 64 (no longer in use)
SCAN 128 Watch font files being scanned to build caches
SCANV 256 Verbose font file scanning information
MEMORY 512 Monitor fontconfig memory usage
CONFIG 1024 Monitor which config files are loaded
LANGSET 2048 Dump char sets used to construct lang values
OBJTYPES 4096 Display message when value typechecks fail
Add the value of the desired debug levels together and assign that (in
base 10) to the FC_DEBUG environment variable before running the
application. Output from these statements is sent to stdout.

LANGTAGS

Each font in the database contains a list of languages it supports.
This is computed by comparing the Unicode coverage of the font with the
orthography of each language. Languages are tagged using an RFC-3066
compatible naming and occur in two parts -- the ISO 639 language tag
followed a hyphen and then by the ISO 3166 country code. The hyphen and
country code may be elided.
Fontconfig has orthographies for several languages built into the
library. No provision has been made for adding new ones aside from
rebuilding the library. It currently supports 122 of the 139 languages
named in ISO 639-1, 141 of the languages with two-letter codes from ISO
639-2 and another 30 languages with only three-letter codes. Languages
with both two and three letter codes are provided with only the two
letter code.
For languages used in multiple territories with radically different
character sets, fontconfig includes per-territory orthographies. This
includes Azerbaijani, Kurdish, Pashto, Tigrinya and Chinese.

CONFIGURATIONFILEFORMAT

Configuration files for fontconfig are stored in XML format; this
format makes external configuration tools easier to write and ensures
that they will generate syntactically correct configuration files. As
XML files are plain text, they can also be manipulated by the expert
user using a text editor.
The fontconfig document type definition resides in the external entity
"fonts.dtd"; this is normally stored in the default font configuration
directory (/etc/fonts). Each configuration file should contain the
following structure:
<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
...
</fontconfig>
<FONTCONFIG>
This is the top level element for a font configuration and can contain
<dir>, <cache>, <include>, <match> and <alias> elements in any order.
<DIR>
This element contains a directory name which will be scanned for font
files to include in the set of available fonts.
<CACHE>
This element contains a file name for the per-user cache of font
information. If it starts with '~', it refers to a file in the users
home directory. This file is used to hold information about fonts that
isn't present in the per-directory cache files. It is automatically
maintained by the fontconfig library. The default for this file is
``~/.fonts.cache-<version>'', where <version> is the font configuration
file version number (currently 2).
<INCLUDEIGNORE_MISSING=NO">"
This element contains the name of an additional configuration file or
directory. If a directory, every file within that directory starting
with an ASCII digit (U+0030 - U+0039) and ending with the string
``.conf'' will be processed in sorted order. When the XML datatype is
traversed by FcConfigParse, the contents of the file(s) will also be
incorporated into the configuration by passing the filename(s) to
FcConfigLoadAndParse. If 'ignore_missing' is set to "yes" instead of
the default "no", a missing file or directory will elicit no warning
message from the library.
<CONFIG>
This element provides a place to consolidate additional configuration
information. <config> can contain <blank> and <rescan> elements in any
order.
<BLANK>
Fonts often include "broken" glyphs which appear in the encoding but
are drawn as blanks on the screen. Within the <blank> element, place
each Unicode characters which is supposed to be blank in an <int>
element. Characters outside of this set which are drawn as blank will
be elided from the set of characters supported by the font.
<RESCAN>
The <rescan> element holds an <int> element which indicates the default
interval between automatic checks for font configuration changes.
Fontconfig will validate all of the configuration files and directories
and automatically rebuild the internal datastructures when this
interval passes.
<SELECTFONT>
This element is used to black/white list fonts from being listed or
matched against. It holds acceptfont and rejectfont elements.
<ACCEPTFONT>
Fonts matched by an acceptfont element are "whitelisted"; such fonts
are explicitly included in the set of fonts used to resolve list and
match requests; including them in this list protects them from being
"blacklisted" by a rejectfont element. Acceptfont elements include glob
and pattern elements which are used to match fonts.
<REJECTFONT>
Fonts matched by an rejectfont element are "blacklisted"; such fonts
are excluded from the set of fonts used to resolve list and match
requests as if they didn't exist in the system. Rejectfont elements
include glob and pattern elements which are used to match fonts.
<GLOB>
Glob elements hold shell-style filename matching patterns (including ?
and *) which match fonts based on their complete pathnames. This can be
used to exclude a set of directories (/usr/share/fonts/uglyfont*), or
particular font file types (*.pcf.gz), but the latter mechanism relies
rather heavily on filenaming conventions which can't be relied upon.
Note that globs only apply to directories, not to individual fonts.
<PATTERN>
Pattern elements perform list-style matching on incoming fonts; that
is, they hold a list of elements and associated values. If all of those
elements have a matching value, then the pattern matches the font. This
can be used to select fonts based on attributes of the font (scalable,
bold, etc), which is a more reliable mechanism than using file
extensions. Pattern elements include patelt elements.
<PATELTNAME=PROPERTY">"
Patelt elements hold a single pattern element and list of values. They
must have a 'name' attribute which indicates the pattern element name.
Patelt elements include int, double, string, matrix, bool, charset and
const elements.
<MATCHTARGET=PATTERN">"
This element holds first a (possibly empty) list of <test> elements and
then a (possibly empty) list of <edit> elements. Patterns which match
all of the tests are subjected to all the edits. If 'target' is set to
"font" instead of the default "pattern", then this element applies to
the font name resulting from a match rather than a font pattern to be
matched. If 'target' is set to "scan", then this element applies when
the font is scanned to build the fontconfig database.
<TESTQUAL=ANY"NAME="PROPERTY"TARGET="DEFAULT"COMPARE="EQ">"
This element contains a single value which is compared with the target
('pattern', 'font', 'scan' or 'default') property "property"
(substitute any of the property names seen above). 'compare' can be one
of "eq", "not_eq", "less", "less_eq", "more", or "more_eq". 'qual' may
either be the default, "any", in which case the match succeeds if any
value associated with the property matches the test value, or "all", in
which case all of the values associated with the property must match
the test value. When used in a <match target="font"> element, the
target= attribute in the <test> element selects between matching the
original pattern or the font. "default" selects whichever target the
outer <match> element has selected.
<EDITNAME=PROPERTY"MODE="ASSIGN"BINDING="WEAK">"
This element contains a list of expression elements (any of the value
or operator elements). The expression elements are evaluated at run-
time and modify the property "property". The modification depends on
whether "property" was matched by one of the associated <test>
elements, if so, the modification may affect the first matched value.
Any values inserted into the property are given the indicated binding
("strong", "weak" or "same") with "same" binding using the value from
the matched pattern element. 'mode' is one of:
Mode With Match Without Match
---------------------------------------------------------------------
"assign" Replace matching value Replace all values
"assign_replace" Replace all values Replace all values
"prepend" Insert before matching Insert at head of list
"prepend_first" Insert at head of list Insert at head of list
"append" Append after matching Append at end of list
"append_last" Append at end of list Append at end of list
<INT>,<DOUBLE>,<STRING>,<BOOL>
These elements hold a single value of the indicated type. <bool>
elements hold either true or false. An important limitation exists in
the parsing of floating point numbers -- fontconfig requires that the
mantissa start with a digit, not a decimal point, so insert a leading
zero for purely fractional values (e.g. use 0.5 instead of .5 and -0.5
instead of -.5).
<MATRIX>
This element holds the four <double> elements of an affine
transformation.
<NAME>
Holds a property name. Evaluates to the first value from the property
of the font, not the pattern.
<CONST>
Holds the name of a constant; these are always integers and serve as
symbolic names for common font values:
Constant Property Value
-------------------------------------
thin weight 0
extralight weight 40
ultralight weight 40
light weight 50
book weight 75
regular weight 80
normal weight 80
medium weight 100
demibold weight 180
semibold weight 180
bold weight 200
extrabold weight 205
black weight 210
heavy weight 210
roman slant 0
italic slant 100
oblique slant 110
ultracondensed width 50
extracondensed width 63
condensed width 75
semicondensed width 87
normal width 100
semiexpanded width 113
expanded width 125
extraexpanded width 150
ultraexpanded width 200
proportional spacing 0
dual spacing 90
mono spacing 100
charcell spacing 110
unknown rgba 0
rgb rgba 1
bgr rgba 2
vrgb rgba 3
vbgr rgba 4
none rgba 5
lcdnone lcdfilter 0
lcddefault lcdfilter 1
lcdlight lcdfilter 2
lcdlegacy lcdfilter 3
hintnone hintstyle 0
hintslight hintstyle 1
hintmedium hintstyle 2
hintfull hintstyle 3
<OR>,<AND>,<PLUS>,<MINUS>,<TIMES>,<DIVIDE>
These elements perform the specified operation on a list of expression
elements. <or> and <and> are boolean, not bitwise.
<EQ>,<NOT_EQ>,<LESS>,<LESS_EQ>,<MORE>,<MORE_EQ>
These elements compare two values, producing a boolean result.
<NOT>
Inverts the boolean sense of its one expression element
<IF>
This element takes three expression elements; if the value of the first
is true, it produces the value of the second, otherwise it produces the
value of the third.
<ALIAS>
Alias elements provide a shorthand notation for the set of common match
operations needed to substitute one font family for another. They
contain a <family> element followed by optional <prefer>, <accept> and
<default> elements. Fonts matching the <family> element are edited to
prepend the list of <prefer>ed families before the matching <family>,
append the <accept>able families after the matching <family> and append
the <default> families to the end of the family list.
<FAMILY>
Holds a single font family name
<PREFER>,<ACCEPT>,<DEFAULT>
These hold a list of <family> elements to be used by the <alias>
element.

FILES

fonts.conf contains configuration information for the fontconfig
library consisting of directories to look at for font information as
well as instructions on editing program specified font patterns before
attempting to match the available fonts. It is in xml format.
conf.d is the conventional name for a directory of additional
configuration files managed by external applications or the local
administrator. The filenames starting with decimal digits are sorted in
lexicographic order and used as additional configuration files. All of
these files are in xml format. The master fonts.conf file references
this directory in an <include> directive.
fonts.dtd is a DTD that describes the format of the configuration
files.
~/.fonts.conf.d is the conventional name for a per-user directory of
(typically auto-generated) configuration files, although the actual
location is specified in the global fonts.conf file.
~/.fonts.conf is the conventional location for per-user font
configuration, although the actual location is specified in the global
fonts.conf file.
~/.fonts.cache-* is the conventional repository of font information
that isn't found in the per-directory caches. This file is
automatically maintained by fontconfig.